1,721,019 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Origin, evolution, and mixing of saline and dilute groundwaters in three regional flow systems, midcontinent, U.S.A.
No full texttextLower Paleozoic strata in southeastern Kansas, southwestern Missouri and northern Oklahoma are predominantly marine carbonates that comprise portions of three regional flow systems. Groundwaters in these three adjacent systems exhibit extreme chemical and isotopic variations that delineate large-scale fluid mixing processes and two distinct mechanisms for the generation of saline fluids. Hydrodynamic and geochemical data closely correlate with geographic location and indicate that each system contains waters of markedly different origins. Results of elemental and isotopic mass balance modeling demonstrate that fluid mixing processes exert a fundamental control on groundwater compositions over the 40,000 km² study area. This quantification of groundwater mixing provides an important basis for determining endmember water compositions and evaluating hydrologic models for these flow systems. The three endmember groundwaters are as follows. 1) Dilute modern-day meteoric waters of the Ozark Plateaus aquifer system, recharged to southern Missouri. The evolution of this groundwater is dominated by interaction with host limestone and dolomite aquifer rocks. 2) Eastward migrating, saline Na-Ca-Cl groundwaters from the northern part of the Western Interior Plains aquifer system in central Kansas. These groundwaters are of meteoric origin with distant recharge areas. Salinity is acquired via the subsurface dissolution of Permian halite and subsequent water-rock interaction with silicate minerals. The chemical signature of these groundwaters, coupled with the presence of brines resulting from the dissolution of Permian halite in central Kansas, allow development of a model for the formation of saline Na-Ca-Cl fluids, a common component of many sedimentary basins. Additionally, the large-scale topographically driven flow of the northern part of this aquifer system is a modem analog for models of similar ancient systems. 3) Na-Ca-Cl brines in north-central Oklahoma. In contrast to the other saline endmember, the geochemical signature of endmember 3 groundwater, integrated with hydrogeologic data, indicate that this groundwater may represent a marine-derived brine from the deep Anadarko Basin.Earth and Planetary Science
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Tracing the input and evolution of municipal water in springs and tributaries of the Bull Creek watershed, Austin, TX
Full text linktextThe conservation of freshwater resources is fundamental in supporting modern society and preserving natural habitats and ecosystems. Deterioration of water quality in urban landscapes and loss of municipal water to leaky water distribution infrastructure are two substantial challenges to water-resource sustainability. I examine the geochemistry of streamwater, municipal water, wastewater, soil, and bedrock from the Bull Creek watershed, a rapidly urbanizing watershed in Austin, Texas, to achieve a better understanding of the processes of geochemical evolution as anthropogenically-sourced water recharges natural systems. Urbanization patterns in the Bull Creek watershed have created a contiguous expanse of urban development that covers roughly two thirds of the watershed, whereas the remaining third is rural, enabling direct comparison between urban and rural streamwater from a single watershed. Results indicate that Na, Cl, K, and SO₄ in urban springs and tributaries are elevated more than two-fold in comparison with rural springs and tributaries. A comparison of Sr concentration and Sr isotopic composition for spring and tributary samples indicates that municipal water and wastewater provide a substantial contribution to the urbanized stream branches of Bull Creek. This water is reactive in the subsurface after it leaks from the municipal system, evolving via a pathway of water-rock interaction with limestone.Earth and Planetary Science
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Geochemical evolution of karst vadose water and brush clearing impacts on recharge in central Texas
No full textGroundwater geochemistry is used to investigate flow paths, water residence times, and rock-water interaction processes, which is especially important in central Texas where groundwater flow is unpredictable and difficult to study due to the anisotropic nature of karst terrains. The first part of this study is a multiyear monitoring study that identifies and quantifies the processes controlling vadose drip water evolution in a cave, Natural Bridge Caverns, central Texas. Three different types of drip water are identified. Group 1 drip sites (n=3) are characterized by strong seasonal variations in Mg/Ca and Sr/Ca that are driven by seasonal fluctuations in calcite precipitation related to winter cave ventilation. Group 2 drip sites (n=4) exhibit correlations between drip water composition (Mg/Ca, Sr/Ca, and ⁸⁷Sr/⁸⁶Sr) and measures of water flux (rainfall and drip rate). Mass balance modeling demonstrates rock-water interactions (i.e., dissolution-reprecipitation processes involving carbonate minerals comprising host Cretaceous carbonate rocks) can account for drip water compositions. Group 3 sites (n=2) exhibit limited geochemical, physical or temporal correlations. Group 3 sites likely reflect a combination of Groups 1 and 2 processes, as drip water composition suggests both varying extents of rock-water interaction and calcite precipitation. The results of this study provide insight on the processes controlling the geochemical evolution of vadose karst waters and can be applied toward uncoding the paleoclimate signals recorded in speleothems. More specifically, in areas where cave-air CO₂ fluctuates seasonally, speleothem Mg/Ca and Sr/Ca variations may serve as chemical indicators of annual laminae, and speleothem growth may be biased. The second part of the study uses changes in drip rate and drip water geochemistry to evaluate the affects of brush clearing on recharge. Brush clearing is commonly used to increase stream and spring flow in central Texas even though it is not clear whether or not brush clearing enhances recharge. Drip rate and drip water composition were monitored every four to six weeks from May 2004 to April 2008. Brush clearing above the cave was conducted from April 2007 to July 2007. Drip rate and drip water compositions were compared at nine drip water sites, five of which are directly beneath an area cleared during this study. There were no changes in drip rate, Mg/Ca, Sr/Ca, or ⁸⁷Sr/⁸⁶Sr at drip sites beneath the cleared area that could be attributed to the brush clearing. The lack of change in drip water compositions and drip rates indicate that the brush clearing did not have a discernible impact on recharge to the cave, and suggests brush clearing does not have an impact on vadose recharge.Earth and Planetary Science
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Travertine deposits as records of groundwater evolution in urbanizing environments
Full text linkUrban development has multiple impacts on groundwater, including changes in patterns of recharge, alteration of groundwater flow paths, and increased water contamination. For the most part, these impacts have only recently begun to be appreciated, and in most aquifers there is a lack of data available on recharge and water quality prior to urbanization for comparison. This lack of data across the period of urbanization makes the prediction of the impacts of future development difficult. I propose that recently deposited spring water calcite (travertine) may provide a proxy record of changing groundwater composition over time. The city of Austin, Texas has undergone a large increase in urbanization over the past 40 years. Because the chemistry of municipal water in Austin is distinctive from the local groundwater, I have examined the possibility that the amount of urban water input to local groundwater recharge can be assessed using the isotopic composition of strontium (⁸⁷Sr/⁸⁶Sr) in combination with elemental concentrations and ratios of Mg/Ca and Sr/Ca. This study examines the current depositional environment of three travertine-depositing springs in the Austin area. It makes use of the modern system, including experimental growth of calcite on artificial substrates in the springs, to interpret a 30-year temporal record provided by one of the three studied springs. Three travertine-depositing springs were studied over the course of one year to examine water chemistry and strontium isotope composition changes on a seasonal basis. Elemental concentrations and strontium isotope ratios remained fairly constant throughout the study year, and showed the influence of urban water in the isotopic compositions of the spring water. Glass plate substrates were employed over a fourmonth time period, to examine monthly changes in travertine growth and isotopic and elemental compositions. Using these substrate experiments, I determine travertine growth rates and effective trace element partition coefficients. These partition coefficients are higher than values determined from laboratory experiments from the literature, indicating that partitioning behavior in natural systems may be different than that of controlled laboratory experiments. Applying these partition coefficients to the travertine temporal record provides a more accurate interpretation of past water compositions. Comparison of stable isotopes of carbon and oxygen between spring waters and plate calcites revealed that the plate carbonates (travertines) are not forming in isotopic equilibrium with their dripwaters. Based on this, interpretation of stable isotope records from these travertines should be treated with caution. Isotopic and elemental analyses were conducted on a spring-fed travertine that preserved 30 years of deposition on a roadcut through Lower Cretaceous marine limestones. The spring is actively precipitating calcite, and appears to have grown continually continually since the excavation of the roadcut. The contributing area to this spring has undergone an increase in urban land use of approximately 40% since 1983. ⁸⁷Sr/⁸⁶Sr data for the travertine and spring waters show a small but resolvable increase over time, from 0.70790 to 0.70797. These values for ⁸⁷Sr/⁸⁶Sr are higher than those for Lower Cretaceous marine limestones, and lower than values for municipal water as well as soil exchangeable Sr. The increase in ⁸⁷Sr/⁸⁶Sr may be accounted for in three ways: 1) Through an increased relative proportion of municipal water input to the groundwater in the spring’s contributing area; 2) Through increased overall recharge in the area, resulting in more water-soil interaction; or 3) A combination of the two. Modeling of karst flow processes (water-limestone interaction and fluid mixing) shows that the trend in elemental ratios and ⁸⁷Sr/⁸⁶Sr may be accounted for by processes of soil water-limestone interaction and mixing with urban waters. Models also indicate that this fluid mixing likely occurs in the epikarst zone, and that urban water may account for as much as 80% of the discharge from the spring. Values for ⁸⁷Sr/⁸⁶Sr in spring waters are likely dampened by limestone interaction during times of low recharge. This model of waterlimestone interaction and urban water mixing implies that urbanization in this particular area resulted in increased recharge and that this recharge may be quantifiable over time. Travertine proxies represent a previously unused resource for examining urban recharge in karst terrains.Earth and Planetary Science
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Trace element incorporation in modern speleothem calcite and implications for paleoclimate reconstruction
Full text linktextTrace element compositions, expressed as ratios relative to Ca (Mg/Ca, Sr/Ca and Ba/Ca), in drip water and modern speleothem calcite were measured at multiple sites within a single cave system (Natural Bridge Caverns) in central Texas. These measurements are used to investigate how water and calcite compositions respond to changes in climate. Drip water trace element ratios respond to changes in climate and in soil, vadose zone and/or in-cave processes, which are in turn influenced by climate. It is commonly assumed that speleothem calcite directly reflects these changes in the drip water composition. To test this assumption, this study quantifies the partitioning of trace elements into speleothem calcite in a natural cave setting. To determine the controls on calcite trace element ratios, empirical partition coefficients (K [subscript D]) for Mg, Sr, and Ba are measured using a unique time series of water and modern calcite geochemistry at two drip sites. One drip site, dominantly supplied by conduit flow, has relatively invariant calcite trace element compositions that reflect correspondingly small variations in drip water chemistry. A second drip site, supplied by a combination of conduit and diffuse flow, exhibits a seasonal change in drip water composition due to changes in cave-air CO₂ concentrations. The drip water seasonality at this site is recorded in the calcite trace element compositions; however the partitioning of Mg/Ca from drip water to calcite is not controlled by the same mechanism(s) that control Sr/Ca and Ba/Ca partitioning. Results of this study indicate that the partitioning of Mg changes with drip water Mg concentration, temperature and location of the calcite relative to the point of drip impact. Calcite Sr/Ca and Ba/Ca ratios are more strongly influenced by changes in cave-air CO₂ that cause changes in CO₂ degassing, affecting calcite precipitation. This element specific partitioning complicates the interpretation of speleothem trace element records, since calcite Mg/Ca and Sr/Ca may not always covary even at drip sites that experience PCP. Although there is a strong correlation between Mg/Ca and Sr/Ca ratios in the drip water at these sites, there is considerable scatter between these two values in calcite. Average K [subscript D] values at both sites fall within the range of previous theoretical and empirical studies and are 0.025, 0.12 and 0.15 for Mg, Sr and Ba respectively. It is important to note that not all trace element partitioning is controlled by the same mechanism, since this has implications for interpretations of hydrologic processes from speleothems.Earth and Planetary Science
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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